At 08:25 PM 8/17/2012, john wrote:
>When I have the headlights On, the left turn signal won't flash and both the
>running red light and the amber light is on at the rear on the left side.
>
>
>
>With headlights Off both turn signals work and you wouldn't even know you
>have a problem.

Without even opening the book this looks like a grounding problem
somewhere.  Start thinking in those terms (+12 appearing at the
ground side of things).

Classic case is the stoplight won't work, and the running light will,
but it goes out when the stoplight should go on.  Reason is that the
mutual ground is open on that fixture; the small running light will
give reasonable light even though it's grounded through a stoplight
filament, over to the other side of the van, through the other
stoplight and down to ground.  But as soon as you put +12 on the wire
between the two stoplights, one of them works and the other pulls the
should-be-grounded sided of the running light up to +12 so net
voltage across the running light is ~0.

More later,
David